/*
 * NULL vs nullptr: nullptr is preferred in modern C++ as it provides a type-safe null pointer.
 *
 * . and -> operators: . is used to access members of an object, -> is used to access members through a pointer.
 *
 * INT_MIN: Represents the minimum value of an int type.
 *
 * using vs #define vs typedef:
 *   using umap = unordered_map<int, int>; // modern way to define type aliases
 *
 * Binary tree traversal order: inorder, preorder, postorder.
 *
 * N usually represents the size or number of elements in a structure or array.
 */
